THE EUROPEAN UNION is expected to side with the Spanish Government on all matters regarding Gibraltar's sovereignty once Britain leaves the bloc, Royal Elcano Institute director Charles Powell warned.

Gibraltar has long been a point of contention between the Spanish and British Government, with Madrid moving in to demand more control over the Rock as part of the Brexit negotiations with the European Union.

Gibraltar has been a British overseas territory since 1704 and support for that status still widely remains on the rock.

Royal Elcano Institute director Charles Powell warned Brussels could now favour the Spanish Government in talks over the sovereignty of Gibraltar as Britain stops being an EU member state.

Mr Powell said: "In a sense, Britain has to accept that from now on the Commission will be on Spain’s side, because Spain is a member and Britain is not."

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Brexit news: Madrid has demanded joint sovereignty over Gibraltar after the UK leaves the EU

Gibraltar became a member of the EU by joining the European Economic Community as part of the United Kingdom in 1973.

The Rock is, however, not part of the EU customs union and VAT area and is exempted from the Common Agricultural Policy.

Gibraltar has held two referendums over the years to establish its residents would rather remain British instead of joining Spain.

But Secretary of State for the European Union Diego López Garrido claimed the Briitish Government's behaviour on Gibraltar was "unacceptable".

Mr López Garrido said London should enter talks with Madrid to discuss the future relations between the two states concerning the Rock.

Britain has to accept that from now on the Commission will be on Spain’s side

Charles Powell

He told BBC Radio 4'sTodayprogramme: "I’m sad about the Brexit. Really I don’t understand why. It’s unacceptable that Britain says ‘no matter about Gibraltar. Business as usual, nothing to talk about.’

"It’s unacceptable. The British Government should negotiate with the Spanish Government about Gibraltar."

Gibraltar remains a major stumbling block that must be overcome during Brexit negotiations and the thousands of workers in both Spain and Gibraltar who cross the border each day will be keenly watching for any developments.

Prime MinisterTheresa Mayhas insisted the Rock’s status is not up for discussion at any point in the Brexit negotiations.

A guideline document agreed between the bloc and the UK in May enshrined that “after the United Kingdom leaves the Union, no agreement between the EU and the United Kingdom may apply to the territory of Gibraltar without the agreement between the Kingdom of Spain and the United Kingdom".